I've been trying out the beta of Cobook, a replacement for AddressBook.app on the Mac. I'm always leery of anything messing with my contact information because it can go wrong in a hurry leaving you with a bunch of mismatched addresses and names.
Cobook has a smart interface where it's able to parse what type of information you're putting in and dumps it in the appropriate field. It can connect to your social media accounts on Facebook, Twitter and LinkedIn and get up to date information like phone numbers, addresses, pictures and other details. Plus it also syncs back to AddressBook.app via iCloud so you're information will still be available on your iPhone/etc.
That last one is nice because it means if you stop using Cobook, you don't have to export and import your data back to AddressBook.app. It'll all be there as well. Cobook just acts as a nicer front end to your address book data.
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I actually find myself using AddressBook.app less and less these days so having a quick menubar icon to access it the few times I do is nice. Plus the integration with Twitter, Facebook and LinkedIn is a nice thing to have for keeping contact information up to date1.
I'll keep trying Cobook for now until they announce pricing and availability. I don't know that I'd pay a bunch for it because, as I said, I don't really use the AddressBook.app right now other than to look up a phone number or email.
It actually seems like it'd be a great bundle with Fantastical, the $19.99 Mac App that allows for a similar style of access to your calendar data through a menubar icon.